This section provides background information that is not necessarily prior art.
Electric motors, in particular of the rotary type, are widely used to drive moving parts, in particular in two opposite directions, by inversion of the polarity of supply signals provided thereto.
For example, in a motor vehicle, electric motors are used in window regulators to drive a vehicle window (or sunroof, or similar element) along two, generally linear, opposite directions, i.e. an opening and a closing direction. Generally, the rotation of a shaft of the electric motor is transformed into a linear movement of the moving part, via a suitable coupling arrangement; therefore, a movement of the moving part corresponds to a rotation of the electric motor, with a given coupling ratio.
A system for determining the position of the moving part driven by the electric motor is required in order to control the movement (e.g. in order to implement a feedback control action); in particular, in case of a motor vehicle window regulator, the control action also has to provide safety features, such as a quick reaction to events that could cause harm to a vehicle passenger (so called anti-pinch feature).
Known position determining systems include incremental position sensors coupled to the electric motor, e.g. magnetic Hall sensors coupled to a shaft of the electric motor, in order to determine an incremental change of position of the moving part (with respect to a previous position), based on the sensed rotation of the electric motor.
The present Applicant has realized that there are at least certain operating conditions, for which determining the position of the moving part driven by the electric motor may prove a difficult task.
In particular, when an electric motor receives a command to stop or reverse its movement, e.g. its rotation, the same electric motor may continue its motion for a certain amount of time, due to the momentum of the driven part coupled thereto. Moreover, it may happen that a mechanical stall of the electric motor causes its motion in a reverse direction with respect to a previous direction of movement.
In order to at least partially cope with these difficulties, known solutions generally envisage use of two or more position sensors coupled to the electric motor, at spaced apart locations, in order to determine its movements in the two opposite directions. In particular, a phase difference between impulses detected by the sensors may be used as an indication of the direction of movement.
However, these systems are quite complex and expensive to manufacture, and arrangement of the two or more position sensors may prove to be critical in certain applications, such as in automotive applications, due to size and costs requirements.